1. Field of the Invention
The present invention relates to a laminated type semiconductor ceramic element, in particular, to a laminated type semiconductor ceramic element having positive temperature-resistance characteristics, and to a production method therefor.
2. Description of the Related Art
It is known conventionally that barium titanate has superior positive temperature-resistance characteristics (hereinafter referred to as the PTC characteristics) with a small specific resistance at ordinary temperatures, and a drastic rise in resistance value at temperatures above the Curie point. Semiconductor ceramic elements containing the barium titanate as the main component are widely applied for demagnetization of cathode ray tubes, temperature control, overcurrent protection, heaters, and the like.
However, for the semiconductor ceramic elements to be used for these applications, a lower resistance at room temperature, a smaller size of the elements, and a higher pressure resistance have been seriously in demand. Japanese Unexamined Application Patent Publication No. 57-60802 discloses a laminated type semiconductor ceramic electronic part to meet the demand. The laminated type semiconductor ceramic part is produced by laminating semiconductor ceramic layers containing barium titanate as the main component, and internal electrode layers made from a Pt-Pd alloy alternately, and baking the same integrally. According to the laminated structure, the electrode area of the semiconductor ceramic electronic part can be drastically enlarged, and thus a small size of the electronic part itself can be achieved. However, there is a problem in that the room temperature resistance value rises in the case in which the internal electrodes are used because ohmic contact with the semiconductor ceramic cannot be realized.
Japanese Unexamined Patent Application Publication No. 6-151103 discloses a laminated type semiconductor ceramic electronic part using an Ni-based metal as the internal electrode material enabling the ohmic contact with the semiconductor ceramic. Since an internal electrode material using an Ni-based metal is oxidized in an ordinary atmosphere, it is necessary to conduct a re-oxidizing process at a temperature so as not to oxidize the Ni-based metal after the baking operation in a reducing atmosphere. Since the ohmic contact of the semiconductor ceramic and the internal electrode can be obtained, the room temperature resistance value rise can be prevented.
However, although the conventional laminated type semiconductor ceramic element has superior values in PTC characteristics and the room temperature resistance value, it is not used in practice due to a low withstand voltage.